The treatment of proliferative disease, particularly cancer, by chemotherapeutic means often relies upon exploiting differences in target proliferating cells and other normal cells in the human or animal body. For example, many chemical agents are designed to be taken up by rapidly replicating DNA so that the process of DNA replication and cell division is disrupted. Another approach is to identify antigens on the surface of tumor cells or other abnormal cells which are not normally expressed in developed human tissue, such as tumor antigens or embryonic antigens. Such antigens can be targeted with binding proteins such as antibodies which can block or neutralize the antigen. In addition, the binding proteins, including antibodies and fragments thereof, may deliver a toxic agent or other substance which is capable of directly or indirectly activating a toxic agent at the site of a tumor.
The EGFR is an attractive target for tumor-targeted antibody therapy because it is over-expressed in many types of epithelial tumors (Voldborg et al. (1997). Epidermal growth factor receptor (EGFR) and EGFR mutations, function and possible role in clinical trials. Ann Oncol. 8, 1197-206; den Eynde, B. and Scott, A. M. Tumor Antigens. In: P. J. Delves and I. M. Roitt (eds.), Encyclopedia of Immunology, Second Edition, pp. 2424-31. London: Academic Press (1998)). Moreover, expression of the EGFR is associated with poor prognosis in a number of tumor types including stomach, colon, urinary bladder, breast, prostate, endometrium, kidney and brain (e.g., glioma). Consequently, a number of EGFR antibodies have been reported in the literature with several undergoing clinical evaluation (Baselga et al. (2000) Phase I Studies of Anti-Epidermal Growth Factor Receptor Chimeric Antibody C225 Alone and in Combination With Cisplatin. J. Clin. Oncol. 18, 904; Fullot et al. (1996): A phase I study of an anti-epidermal growth factor receptor monoclonal antibody for the treatment of malignant gliomas. Neurosurgery. 39, 478-83; Seymour, L. (1999) Novel anti-cancer agents in development: exciting prospects and new challenges. Cancer Treat. Rev. 25, 301-12)).
Results from studies using EGFR mAbs in patients with head and neck cancer, squamous cell lung cancer, brain gliomas and malignant astrocytomas have been encouraging. The antitumor activity of most EGFR antibodies is enhanced by their ability to block ligand binding (Sturgis et al. (1994) Effects of antiepidermal growth factor receptor antibody 528 on the proliferation and differentiation of head and neck cancer. Otolaryngol. Head Neck. Surg. 111, 633-43; Goldstein et al. (1995) Biological efficacy of a chimeric antibody to the epidermal growth factor receptor in a human tumor xenograft model. Clin. Cancer Res. 1, 1311-8). Such antibodies may mediate their efficacy through both modulation of cellular proliferation and antibody dependent immune functions (e.g. complement activation). The use of these antibodies, however, may be limited by uptake in organs that have high endogenous levels of EGFR such as the liver and skin (Baselga et al., 2000; Fullot et al., 1996).
A significant proportion of tumors containing amplifications of the EGFR gene (i.e., multiple copies of the EGFR gene) also co-express a truncated version of the receptor (Wikstrand et al. (1998) The class III variant of the epidermal growth factor receptor (EGFR): characterization and utilization as an immunotherapeutic target. J. Neurovirol. 4, 148-158) known as de2-7 EGFR, ΔEGFR, or Δ2-7 (terms used interchangeably herein) (Olapade-Olaopa et al. (2000) Evidence for the differential expression of a variant EGF receptor protein in human prostate cancer. Br. J. Cancer. 82, 186-94). The rearrangement seen in the de2-7 EGFR results in an in-frame mature mRNA lacking 801 nucleotides spanning exons 2-7 (Wong et al. (1992) Structural alterations of the epidermal growth factor receptor gene in human gliomas. Proc. Natl. Acad. Sci. U.S.A. 89, 2965-9; Yamazaki et al. (1990) A deletion mutation within the ligand binding domain is responsible for activation of epidermal growth factor receptor gene in human brain tumors. Jpn. J. Cancer Res. 81, 773-9; Yamazaki et al. (1988) Amplification of the structurally and functionally altered epidermal growth factor receptor gene (c-erbB) in human brain tumors. Mol. Cell. Biol. 8, 1816-20; Sugawa et al. (1990) Identical splicing of aberrant epidermal growth factor receptor transcripts from amplified rearranged genes in human glioblastomas. Proc. Natl. Acad. Sci. U.S.A. 87, 8602-6). The corresponding EGFR protein has a 267 amino acid deletion comprising residues 6-273 of the extracellular domain and a novel glycine residue at the fusion junction (Sugawa et al., 1990). This deletion, together with the insertion of a glycine residue, produces a unique junctional peptide at the deletion interface (Sugawa et al., 1990).
The de2-7 EGFR has been reported in a number of tumor types including glioma, breast, lung, ovarian and prostate (Wikstrand et al. (1997) Cell surface localization and density of the tumor-associated variant of the epidermal growth factor receptor, EGFRvIII. Cancer Res. 57, 4130-40; Olapade-Olaopa et al. (2000) Evidence for the differential expression of a variant EGF receptor protein in human prostate cancer. Br. J. Cancer. 82, 186-94; Wikstrand, et al. (1995) Monoclonal antibodies against EGFRvIII in are tumor specific and react with breast and lung carcinomas and malignant gliomas. Cancer Res. 55, 3140-8; Garcia de Palazzo et al. (1993) Expression of mutated epidermal growth factor receptor by non-small cell lung carcinomas. Cancer Res. 53, 3217-20). While this truncated receptor does not bind ligand, it possesses low constitutive activity and imparts a significant growth advantage to glioma cells grown as tumor xenografts in nude mice (Nishikawa et al. (1994) A mutant epidermal growth factor receptor common in human glioma confers enhanced tumorigenicity. Proc. Natl. Acad. Sci. U.S.A. 91, 7727-31) and is able to transform NIH3T3 cells (Batra et al. (1995) Epidermal growth factor ligand independent, unregulated, cell-transforming potential of a naturally occurring human mutant EGFRvIII gene. Cell Growth Differ. 6, 1251-9) and MCF-7 cells. The cellular mechanisms utilized by the de2-7 EGFR in glioma cells are not fully defined but are reported to include a decrease in apoptosis (Nagane et al. (1996) A common mutant epidermal growth factor receptor confers enhanced tumorigenicity on human glioblastoma cells by increasing proliferation and reducing apoptosis. Cancer Res. 56, 5079-86) and a small enhancement of proliferation (Nagane et al., 1996).
As expression of this truncated receptor is restricted to tumor cells it represents a highly specific target for antibody therapy. Accordingly, a number of laboratories have reported the generation of both polyclonal (Humphrey et al. (1990) Anti-synthetic peptide antibody reacting at the fusion junction of deletion mutant epidermal growth factor receptors in human glioblastoma. Proc. Natl. Acad. Sci. U.S.A. 87, 4207-11) and monoclonal (Wikstrand et al. (1995) Monoclonal antibodies against EGFRvIII are tumor specific and react with breast and lung carcinomas and malignant gliomas; Okamoto et al. (1996) Monoclonal antibody against the fusion junction of a deletion-mutant epidermal growth factor receptor. Br. J. Cancer. 73, 1366-72; Hills et al. (1995) Specific targeting of a mutant, activated EGF receptor found in glioblastoma using a monoclonal antibody. Int. J. Cancer. 63, 537-43) antibodies specific to the unique peptide of de2-7 EGFR. A series of mouse mAbs, isolated following immunization with the unique de2-7 peptide, all showed selectivity and specificity for the truncated receptor and targeted de2-7 EGFR positive xenografts grown in nude mice (Wikstrand et al. (1995); Reist et al. (1997) Improved targeting of an anti-epidermal growth factor receptor variant III monoclonal antibody in tumor xenografts after labeling using N-succinimidyl 5-iodo-3-pyridinecarboxylate. Cancer Res. 57, 1510-5; Reist et al. (1995) Tumor-specific anti-epidermal growth factor receptor variant III monoclonal antibodies: use of the tyramine-cellobiose radioiodination method enhances cellular retention and uptake in tumor xenografts. Cancer Res. 55, 4375-82).
However, one potential shortcoming of de2-7 EGFR antibodies is that only a proportion of tumors exhibiting amplification of the EGFR gene also express the de2-7EGFR (Ekstrand et al. (1992) Amplified and rearranged epidermal growth factor receptor genes in human glioblastomas reveal deletions of sequences encoding portions of the N- and/or C-terminal tails. Proc. Natl. Acad. Sci. U.S.A. 89, 4309-13). The exact percentage of tumors containing the de2-7 EGFR is not completely established, because the use of different techniques (i.e. PCR versus immunohistochemistry) and various antibodies, has produced a wide range of reported values for the frequency of its presence. Published data indicates that approximately 25-30% of gliomas express de2-7 EGFR with expression being lowest in anaplastic astrocytomas and highest in glioblastoma multiforme (Wong et al. (1992); Wikstrand et al. (1998) The class III variant of the epidermal growth factor receptor (EGFR): characterization and utilization as an immunotherapeutic target. J. Neurovirol. 4, 148-58; Moscatello et al. (1995) Frequent expression of a mutant epidermal growth factor receptor in multiple human tumors. Cancer Res. 55, 5536-9). The proportion of positive cells within de2-7 EGFR expressing gliomas has been reported to range from 37-86% (Wikstrand et al. (1997)). 27% of breast carcinomas and 17% of lung cancers were found to be positive for the de2-7 EGFR (Wikstrand et al. (1997); Wikstrand et al. (1995); Wikstrand et al. (1998); and Hills et al., 1995). Thus, de2-7 EGFR specific antibodies would be expected to be useful in only a percentage of EGFR positive tumors.
Thus, while the extant evidence of activity of EGFR antibodies is encouraging, the observed limitations on range of applicability and efficacy reflected above remain. Accordingly, it would be desirable to develop antibodies and like agents that demonstrate efficacy with a broad range of tumors, and it is toward the achievement of that objective that the present invention is directed.
The citation of references herein shall not be construed as an admission that such is prior art to the present invention.